My shower is smaller than 4x6 but we have the door on the short end, controls on the longer wall and a bench at the back. So if I am understanding you correctly you setup should look like mine only a little bigger. It works great for us. Make sure you hand shower is mounted close enough to the bench so it can be used while sitting on the bench.

Back onto the OP question, I don't believe moving from 2x4 to 2x6 should be as costly as your architect believes. MacV's breakdown is much more accurate from my experience. 2x6's were around $1 more per 10ft in my area, so the extra lumber bill was in the $3,000 range. If you order the windows and doors from the manufacturer with the jambs built for 2x6, the extra cost is minimal, something like $20 per window or door (maybe $50 for doors). Insulation, well you can spend as little or as much as you want, but striking the balance between air infiltration and price is the center of most debates. R value is great in a lab, but in the real world, you need your doors and windows to shut tight and keep the walls from allowing wind in. Worthy's mention of an exterior foam board (taped at the seams) coupled with a blown in cellulose or fiberglass is a great economical choice. He's also right about the interior walls, I should have done 2x6 there as well. You really can't insulate around the DWV pipes for sound in a 2x4 wall.

I would go with 1 or 2 regular shower heads and 1 handshower on a slide bar. The handshower on the slidebar comes in handy for shaving legs, showering kids and for cleaning the shower. How many regular shower heads you have will also depend on shower setup (i.e. door placement). The rainshower head mounted on the ceiling is a personal preference thing. We have one and DH does not like it (even though he was the one that specced it). I use it at the end of my shower as a refresher--I run it just long enough for the cold water to dissipate through while the warm regular shower is still running, then I turn them both off. DS2 loves having the rainshower, the regular shower and the handshower going all at once on him (keep in mind he's only 7)--although it does make it feel spa-like without all those wall jets that require so much water pressure and volume. Hope this helps!

omeyers, We are in Illinois. We build a 1800 s.f. home for us about 6 years ago and used Icynene (foam insulation) on 2x4 walls. We loved it! I think the savings were not that good in this size of homes, they say that homes bigger thn 3,000 s.f. get better savings. I liked the fact of knowing there was no fiber glass flying around (usually the insulation they pace at the rim joist is exposed) We sold the house last year pretty fast (1 month)and the insulation was a good factor. Last year we built another house for us, 2,500 s.f. and used 2x6 and blow in Spider Insulation with R-23 (DH just wanted to try something different). I loved the fact that it was a formaldehyde free insulation. DH wanted to see what people thought about the house (he is retiring in about 6 years and we will move down south)and we had an open house prior the closing - we received an offer the same day and decided to sell the house :( (we paid $5,000 and the attic was R-49) Now we need a house for us and getting ready to start building. The thing is, the foam insulation is just R-13 (officially) and they claim it performs a lot higher than that because it seals better (and it's true). DH wanted to try it again and the bid was 13,000. We supposely save in wood studs, vapor barrier and window extensions but still it is about 40% higher than the SPIDER. The way I see it, when promoting the house to sell it, isn't it better to say that the house is 2x6 with R-23 formaldehyde free than saying we have a 2x4 with R-13 -but very marbelous insulation? oh and the foam insulation people say that incresing the stud to 2x6 does not help and the price will be double!!! What do you guys think? we are still deciding. see the attached link, it healps to know what R-value to use depending on location Here is a link that might be useful: Energy Efficiency