I was wondering if anyone has any opinions on the uses of 'PHP include' 'SSI' or DW library items, for common site elements.

I'm currently using DW library items and am considering a switch to either of the above. However I'm just a little concerned this could slow my pages quite a bit. Currently my pages download extreamly fast, which I put down to the fact that the pages are simply single HTML pages, plus 'stacked tables' (for apparent speed). However, the problem with lib's is that when altered, every page they refer to have to be uploaded (which gets a pain).

I would like to know:

a) If there is any difference in speed between using SSI and PHP include.

b) How much does a single SSI/Include add to the total download time? - Are we talking say 0.5 secs for 1 call?

c) Does the use of say 2 SSI/Include = to the additional download time of 2x the additional download time of 1SSI/Include - ie. is it proportional.

I hope someone can put my mind at rest and advise of what would be the best option.