I doubt you'll really benefit from the better graphics chip on the T61p judging by your usage patterns. I also don't think you need the super high resolution screen option on the T61p because things will be tiny.

I have a T42p with a 14" screen at 1400x1050 resolution and that's about as small on text size (or as big on DPI) as I'd go. The 1680x1050 resolution is what my 22" LCD monitor displays (and my eyes are quite happy with it). Shrinking that down to a 15.4" screen would make the text about the same size as my T42p.