If you want real high-speed 3G, then a true HSDPA 3G is whay you should look for. and that is what the N95 supports with american frequencies (At&T).

The Nokia 6555 on the other hand supports upto UMTS bands - which is slightly slower than HSDPA. So it all depends on what you are looking for.

When the N95-3 dropped in price, I bought one recently, and surfing on the Nokia N810 with HSDPA connectivity has been very good. I wanted HSDPA since I use Video chat a lot on my n810 (Gizmo / Google Talk client) and this is where HSDPA speeds come up as a big winner.

Also the N95 5 MP camera is really a treat for me - since I don't have to carry a pocket camera separately (just for casual photography).

But its real difficult to justify an expensive N810 and then an expensive phone like the N95 to add connectivity to it. I wish there were cheaper US 3G (HSDPA) phones from Nokia.