Actually, the PowerVR release is irrelevant to the tablets.

Although the N800/N810 are built around an OMAP2420 they don't use the PowerVR on the chip. The reason is that it only comes with 5Mbits of VRAM which is nowhere near enough for the 800x480x16 resolution. So Nokia had to use an external LCD controller (Epson Blizzard or Hailstorm I think), which is the reason for the not so great video performance (bandwidth to/from the CPU is slow).

The OMAP3430 will support resolutions up to 1024x768x24, so next year's tablet (the one after the N810) is likely to finally have hardware-accelerated 3D and possibly a higher-res screen as well (why else would they spend time making hildon resolution-independent earlier this year?)