Welcome to the site. Check out the gallery section here. Our member; bygracealone is currently working on repowering his dual console from a SeaDrive to a bracket/outboard conversion. Also in the gallery section is several years of factory catalogs with specs. Depending on the year of your boat, most were rated to 235 HP or so.
Just be prepared to post some photos of your rig as members here will begin to bombard you with the pic requests. 8)
Thanks. Mine wants to look as nice as yours when it grows up
Before I answer your question, keep in mind that I have yet to even ride in a V20! However, with that caveat, I would say that you should stick with the 175. Personally, I would have preferred a 150. The only reason I went with the 200 was because the price was right. At the time, I couldn't find a 150 for the price I paid for the 200. A 175 will be more than adequate for your boat.