[CentOS] ext4, 4k sector alignment

I've mentioned this problem before but put off doing anything about it 
and maybe now someone can suggest the best solution.

I have a 3-member RAID1 set where one of the members is periodically 
swapped and rotated offsite.  The filesystem contains a backuppc archive 
which has millions of hardlinks that make it impractical to copy with a 
file-oriented approach.  The current filesystem is ext3 with one 
partition that uses the entire disk capacity (no lvm).  It works as is, 
but...

I'd like to use a laptop size drive for the swapped member and the only 
ones available that match the size have 4k sectors.  I have swappable, 
trayless SATA bays available for both drive sizes.  The problem is that 
with the current partition layout, the drive with 4k sectors takes more 
than a day to re-sync even though on read access the speed is a match 
for the full sized drives that sync in a few hours.

My questions for any filesystem experts are:

Is there a way to adjust the existing md partitions to get the right 
alignment for 4k sectors without having to do a file-oriented copy to 
new partitions?  A resize + a dd copy to shift the position might be 
feasible time-wise if that would work.

Is it worth converting to ext4?

Is there a difference between doing this on 5.6 or 6.x?

If I start over from scratch with 6.x, will the partitioning tools 
automatically align for 4k sector drives (with/without lvm?)?

-- 
   Les Mikesell
    lesmikesell at gmail.com