X2; upgrading to the I6 is just not worth the amount of work that will need to be done... Also, there are plenty of things that you can do to a 4 banger to make it run stronger and that are easier than an engine swap. Some guys in other forums have installed supercharges, turbos, and one guy did a sixty over bore, and increased compression to increase power... You can also FREE UP some power by doing some simple conversions (eFan, etc.).