Perry miniatures are a bit slighter than
GW heroic scale models. They wouldn't necessarily look terrible next to your other
GW models though. Take a look at this website:
http://www.fysh.org/~katie/pictures/miniature-compares/
You want the first picture in the second row. The miniatures are just about the same size, but the Perry models are less "heroic," although the proportions are not true to scale. You will also find that the Perry models are not as flamboyant as the
GW empire models. The sculpts are very well researched and for the most part historically accurate. Even so, you can find many rather empire-ish models in their ranges.
On a side note, I have had nothing but positive experiences with Perry models. Perry is my favorite miniatures company, even though I don't play historical wargames. I use Perry models for
IG conversions and for Mordheim models. Perry's products are almost always a fantastic experience from opening the box to putting a fully finished model on the table. On top of that, the new plastic box sets include sprues that often have neat bits and clever little options. They are also very easy to convert. I cannot recommend Perry highly enough.
Edit: You can also take a look at this thread on Warhammer Empire:
http://warhammer-empire.com/theforum/index.php?topic=6724.75