The 827 would make a good replacement for your Imax, if the current antenna failed. However, the difference in performance would not warrant the replacement alone. Distant signals may increase a little due to the 827's ground plane radials that also reduce common mode currents but, I wouldn't do it unless there was a problem.
If you buy an 827, be sure to tighten the 3 set screws that make contact with the matching coil. The middle, center tap hex screw is hidden under the 8mm bolt, which must be removed first. In some cases, they are not tight enough to insure long term connection with a stable VSWR.