No, there wouldn't be a problem with blade tip speed due to it being a 2-blade 42" deck.
Other factors would have to be present in deck gearing to slow the tip speed.
It should have just as much tip speed as a 60" class mower.
Same thing, one less blade.
Now, with that said, no it should not bog easy with ample horsepower.
To be honest with you, I have played with these theories a lot in the field.
Turns out the decks with shorter blades seem actually tend to bog easier.
This is because the shorter the blade, the higher required gearing to attain the same BTS.
For instance, a 3 blade 48" deck seems to pull down much easier than a 2 blade 42"
envy, I would say that you notice it does not bog as much, because there is a lot more leverage put out at the tip of the blade, and a lot more mass behind it.
but, you get a lot more rpms, which is what really counts, not tip speed. afterall, you can have a 19,000fpm tip speed, but if the blade is so large that it only does 1 rpm, it is not going to cut very much grass.
I have noticed with my quick 36, that if you have a very over grown patch, it will bog the blades down for about a second, then they will quickly regain their speed, due to the small length, which gives them faster acceleration. if I go through such growth with my exmark, it has two catagories, 1. it kills the engine. 2. the momentum carrys it through, but it comes back up to speed slower.
overall, I would say that for mulching, a medium width blade is best. when the blade is too small, it gets so many rpms going that it makes the clippings dust, and then if it is wet, they make turds. but I think that the small blades are exellent for discharge and leaves. it really chops them up fine.
Yeah, this can become a pretty deep subject matter. Probably deeper than I should attempt to discuss very much at this time of night.
Anyways, it's a funny thing, which can also all be very relevant to setups, actuals and the relative actual equations that go along with them. But, just generally speaking, if for example you take the following in comparison...
If all 4 start with the same size drive pulley and a similar HP to Deck Size ratio, here is what I believe you would find...
To begin with I think you would find that what you find to be true about the Quick 36 is because it's cutting width, length of blade and spinning mass cause it to fall outside of the drag window you get into with a 3 blade 48"
On the other hand, I believe you would find the other decks to be fairly comparable. This is because the spindle pulley size would be the same on the 42" and 60" and only slightly smaller on the 52" to attain the same tip speed.