This was the first result found using my preferred World Wide Web search engine and the search term: PGT25+G4
DLE stands for Dry Low Emissions, and it's the aero-derivative version of DLN (Dry Low NOx). It includes additional fuel control valves, and I think the combustors are multi-zone (at least they were in the early days of development).
SAC stands for Single Annular Combustor, and it's usually a simple, single annular combustor with one combustion zone. To achieve low NOx emissions it's usually necessary to use water- or steam injection (which adds somewhat to the complexity of the auxiliaries).
Other than that, I believe they are basically the same engine--one has the DLE combustion system for low emissions without water- or steam injection (at least for gas fuel), and the other is a "plain" combustion system which must use water- or steam injection for low emissions.
Hope this helps!
By the way, I also found this site (which I personally hadn't run across before):
Looks like a good way to quickly compare lots of different products for lots of different manufacturers.