I'm trying to find a rod blank offered by Loomis or St. Croix that would closley match the Shimano Crucial IM9.  

I Know Loomis GTX and St. Croix Legend Elite are probably the best you can buy for sensitivity.  Not sure I need something that good  or to spend that much to match the Crucial sensitivity.

Can anyone steer me to the quality blank I should be looking at in Loomis or St Croix lines.  I was looking at the Rainshadow RX7 line but am not sure if that is a good blank with sensitivity to match the Crucial (much cheaper than either the Loomis or St. Croix).  But figuring most guys build with Loomis or St. Croix, you would know which type of blank to recommend from those two makers.

Thanks in advance for any guidance.

Be careful not to judge blanks on price alone.  Loomis and St. Croix are about the only 2 companies with a strong enough brand image to charge what they do for blanks.  I've also built on (RX-6 and) RX-7 and I can absolutely promise you that they are better quality than the price suggests.  I would go so far as to say that the RX-7 line might one of the best "values" in blanks today. (at retail price)

Back to your original question- I think GL-2 or SCII would be the closest equivalent to the crucial.  The GL-2 and SCII blanks are about $70- $80.  If I was buying at retail price and looking to replace a crucial, I would buy RX-7 over GL-2 and SCII all day long.  (and spend the extra money upgrading components)

Last consideration- from a builder's perspective the Batson Warranty is tops.  When you don't have to send in the whole rod (just cut out the break plus a couple inches on each side) you save money and hassle.

Just one guy's opinion.