I don't have the specs, but having tried both, the True Fit is roomier. Also, the True Fit gives you 5 more pounds to rear-face (RF to 35 pounds in True Fit, Boulevard RF to 30 pounds). This may matter to you if you have a heavier child that will outgrow the seat RF in weight before height.
The TF is also going to provide more height in the harness - probably about 1" more in actual use. Since most seats are outgrown by height before weight, I'd definitely factor that into the equation.
Do you have a store near you that you can try both seats out and see how they fit in your car? Zellers should have the TF in stock if your local TRU/BRU doesn't, and a local baby boutique should also have the Blvd if your TRU/BRU is out of stock on it.
I much prefer the TF over the Britax convertibles - it is much roomier in the interior, has 5lbs more in the rf'ing weight limit, and has a deeper shell so I suspect it provides just as much SIP as the BLVD and definitely more than the MA at any rate.
But try them for yourself and decide after that. You might find you like the BLVD better - we all have different likes/dislikes in a seat & not every seat works in every vehicle. :thumbsup: