There are lots of little differences (pins vs. bolts used in construction, pressed on vs. bolted on sprokets, etc.) between the Romeo and the Windsor blocks, if you want the details do a search online. Some people feel the Windsor blocks are stronger, part of this is is due to the fact that the Windsor blocks are usualy used in light trucks and Romeo's are usualy used in passenger cars. The reason the Windsor engines were used in the 99 & 00 GT had to do with a shortage of Romeo blocks due to a fire at the Romeo plant.
Ike
p.s. The 01+ Romeo engines have a slightly higher compression ratio than the 99 & 00 Windsors, this caused many of the first 01's being supercharged to blow up due to the tuners not being aware of the compression change (again adding to the feeling the Windsors are stronger)