Any Residential HVAC Experts?

[Cirerrek]

Time to replace my furnace, I've got a contractor lined up, but I've got a bit of dilemma on the equipment selection. Figured I would take shot here to see if anyone might be able to answer my question.

Had a Heat Loss/Heat Gain calc done:

BTUH Loss: 74654
BTUH Gain: 39651

Furnace:

I'm looking at a two stage variable speed furnace which specs out an 49,000/73000 BTUH. So just short of the 74654 mark.

Should I bump up to the 62,000/93000 BTUH unit?

A/C:

I'm looking at a 13 SEER 3 ton/36,000 BTUH unit, again short of the 39651 mark.

Should I bump up to the 13 SEER 3.5/42,000 BTUH unit?

Keep in mind that the load calc was performed on an old house, with plaster on structural brick for insulation (or no insulation, depending on how you look at it )

Any advice would be greatly appreciated.

Thanks,
Cirerrek