Actually, high CRI isn't too useful for the plants, very high CRI(>90) benefits your eyes more than the plants (because it makes plants & fishes look more natural). Higher CRI means less lumens. A PL tube with CRI ~80 is fairly enough. Sometimes just the model no. can tell the spec. of the PL tubes.
e.g. Philips 865 PL :8=CRI>80 65=6500K color temp. 840 8=CRI>80 40=4000K vice versa.
However, it just applies to well-known brand.
BTW, if you want to add a blue tube but don't want to sacrifice your current PL tubes, you can add a T4 or T5 8W FL tube. 8w T5 FL tube is 9.5" long while 8W T4 is 13.5", both are just 1" wide (including the electronic ballast). But there is no power switch on the fixture, you need to do some wiring and beware the safety when placing over the aquarium.
Here are some references for you:
http://www.aquabonneville.org/ligforthefreaqu.html
http://www.landlite.com/catlist.asp?cla ... Nclassid=5
http://www.lighting.philips.com.cn/pro_ ... eiyiti.htm