There is a lake by my house with a 190hp limit. So I'm considering getting a 175 horse.  What kind of speed w difference would I see on a 19ft bas boat between a 175 and a 200

No way we can answer that. Setup makes all the difference.

Prop

Prop height

Load

weather

Weight

Hull design

Jackplate (Yes/No)

You see where I'm going with this? Plenty more needed than this.

id buy a few 175 stickers and keep the speed down....

All other things being equal, you should not lose more than 5-8 mph top end.  Your biggest loss will be in the hole shot.  To make up for the loss in hole shot you will either need to change props which will result in an even lower top end or add a hydrofoil.

The horse power is not where you will see the biggest difference, the torque is where the difference will show, big time. Torque is what gets you up on plane and going with a load.

Most manufactors use one size power head for a for their V-6 motors below 200hp and another, larger power head for motors rated at 200 hp and more. There is no substitution for cubic inches to make torgue.

As for more HP more speed, as mentioned, there are too many variables. A light, fast hull, produces much more gain per hp than a heavy, high drag hull, that may only give a couple more mph.

Now, as for changing decals on a 200 to 175, there is usually a noticable physical size difference between the two that most people knowing anything about them can easily see. Then the data plate is going to have a model/serial number that's going to specify the hp if they ever checked it. Not real sure I would want to get caught with that setup.

K thanks guys. I hate to give up the HP. But the lake is 3  minutes from my house. It's 150 acres and has a lot of nice bass in it.  It's a great place to go during the week cuz lake of the Ozarks and Truman that I fish every weekend are 1 1/2 and 2 hours away. 

I have 2 other 1000 acre lakes here in town as well but they don't have the same quality of bass the other does.

I'm gonna be jumping from a heavy 1985 fiberglass bass tracker with a 90 HP  so I'm sure even the 175 holeshot will seem awesome to me. 

Time in transit on a 150 acre lake won't be much different regardless of the difference between a 175 and a 200.

The horse power is not where you will see the biggest difference, the torque is where the difference will show, big time. Torque is what gets you up on plane and going with a load.

Most manufactors use one size power head for a for their V-6 motors below 200hp and another, larger power head for motors rated at 200 hp and more. There is no substitution for cubic inches to make torgue.

As for more HP more speed, as mentioned, there are too many variables. A light, fast hull, produces much more gain per hp than a heavy, high drag hull, that may only give a couple more mph.

Now, as for changing decals on a 200 to 175, there is usually a noticable physical size difference between the two that most people knowing anything about them can easily see. Then the data plate is going to have a model/serial number that's going to specify the hp if they ever checked it. Not real sure I would want to get caught with that setup.

I might be wrong, but didn't Mercury make a 2.4L 175 HP?

There also might be some 175HP with 2.5L blocks.

I have always been told as a general rule of thumb that 5hp will get you 1MPH faster.  So you'll likely lose around 5mph.  but like others have said, you'll notice the loss in your holeshot, but if your propped correctly you should still be alright.

The only down fall to the 175 Merc 2.5 liter or i should say anything smaller then the 200hp was that the 175hp and down is what they call slot motors they have slots cut in each cylinder to help with the idle of the motor but that made the motor lose torque on the lower end and you would have to run a smaller pitch prop on the heaver boats to help get out of the hole.a Mercury built every thing from a 150hp to a 300 drag using the 2.5 liter block  the only difference was the port timing  and the way the exhaust chest was cut

The horse power is not where you will see the biggest difference, the torque is where the difference will show, big time. Torque is what gets you up on plane and going with a load.

Most manufactors use one size power head for a for their V-6 motors below 200hp and another, larger power head for motors rated at 200 hp and more. There is no substitution for cubic inches to make torgue.

As for more HP more speed, as mentioned, there are too many variables. A light, fast hull, produces much more gain per hp than a heavy, high drag hull, that may only give a couple more mph.

Now, as for changing decals on a 200 to 175, there is usually a noticable physical size difference between the two that most people knowing anything about them can easily see. Then the data plate is going to have a model/serial number that's going to specify the hp if they ever checked it. Not real sure I would want to get caught with that setup.

I might be wrong, but didn't Mercury make a 2.4L 175 HP?

There also might be some 175HP with 2.5L blocks.

Mercury made 2.0 liter blocks from 135hp i think right on up to 225hp motors

And the 2.4 liter was 135hp up to the 200plus hp bridge port motor

and the 2.5 liter was built right on up to 300hp drag motors