i am not a 410a fan as of yet have been schooled on and can service it and insall it just dont trust anything new till it proves itself out. there is a drop in replacement for 22 already on the marget and it is almost the same.i was reading about it in industrie mag. think it is made by hot shot. it also can replace 410a
back to the real question yes replace the intire system if will be to your best interest in the long run. 13seer will also save you monie to run. as far as witch freon to me doesnt matter at this time r22 is still my choice till i have non. for fact once the system is installed and as long as it is done right and no leaks you should never have to ajust the charge again for the life of the unit.