Well, let's take a look at this.
Is your primary purpose to get a Conroe? If so, why bother building a new rig NOW so that you can upgrade to a Conroe in 5 months or so? I mean, as was mentioned, if you have the money, sure go for it. Otherwise, just wait for Conroe and build your new system then.
If you still want to do it anyway, you can save some money by getting the 920 or 930 chip instead of the 950. You will get awesome performance out of the 920 without the cost. I have mine at 3.9 stable now, the only thing keeping me from 4Ghz is crappy temps, pauldovi has his water cooled up to like 4.3 stable and it can go higher.
Also, if you want to buy NOW and plan to upgrade to Conroe, get the ASUS P5WD2-E-Premium motherboard. It OCs like mad, and if any current 975 based board will run Conroe with only a BIOS flash, it will be that one (IMHO).