I can't really tell the difference in speed between the 'standard' and 'high speed' SD cards. There may be a little, in so much as that the camera seems to display the preview almost instaneously with a high speed card rather than after a fraction of a second with a standard card, but you have to be actually watching the LCD quite deliberately to spot it. As you say you don't intend on doing lots of burst mode photography, I really wouldn't pay much of a premium for a high speed card. Although the price gap is narrowing quickly so it may be worth considering if it only involves an couple of extra $$s or so.
In terms of capacity, I advise against paying top dollar for the biggest 2 gig cards. You pay more per megabyte in the first place and they may give up the ghost or get lost just the same. Here in the UK, I can buy 512MB, 'semi-fast' (I forget the read and write speeds, but they're somewhere between standard and fast), Toshiba manufactured cards for about £13 or so. Similar quality 1GB cards come for roughly the same £ per MB ratio at almost £30. Then the price jumps to £85 or more for 2GB, which is why I don't bother.
Unless you're planning marathon trips involving epic photography sessions, 1GB will hold as many pictures as you're likely to want or need to take before you can get to a PC anyway.