Fitting aerobars rather than bar ends will make you more aerodynamic. Bar ends enhance the parchute effect, but with aerobars, the air goes on the outside of your arms. You wont loose any efficiency over drop bars, just the variety of positions.
The limiting factor for the big ring is the curvature of the outside of the front mech. MTB mechs have a smaller radius, but yours may just cut it.
When you are comparing ratios, use gear inches for measuring the gear, and factor in the size of your wheels (inc tyres). A 53 ring is std on road bikes, but is too high for most riders. You have smaller wheels (which give a lower overall gear for a given cog combo) so it may be OK.
Swapping from biopace to round will enable you to spin at a higher cadence, so you may not need a really big ring.