Mount with "nodelalloc". I have servers which host quite a few Cobol C/ISAM files. I was uncomfortable with the very idea of delayed allocation. But the EXT4 delayed allocation cheer-leading section, headed by Ted T'So, convinced me that after 2.6.30, it would be OK.
The very first time we had an power failure, with a UPS with a bad battery, we experienced corruption in several files of those files. Never *ever* *ever* had we experienced such a thing with EXT3. I immediately added nodelalloc as a mount option, and the EXT4 filesystem now seems as resilient as EXT3 ever was. Note that at around the same time as 2.6.30, EXT3 was made less reliable by adding the same 2.6.30 patches to it, and making data=writeback the default journalling mode. So if you do move back to EXT3, make sure to mount with data=journal.
BTW, I've not noted any performance differences mounting EXT4 with nodelalloc. Maybe in a side by side benchmark comparison I'd detect something.