Definitely worth the try. Your biggest enemy may be 12.4 IOS. It's bloated and buggy in my experience, but that has mostly been edge services. If 12.4 pegs your processor, you may want to check the software/hardware matrix and see if one of the older 12.0/2 service provider trains that they continued to add support for (probably some large customer's special requests). I don't know if it will support the G1, but if so, you might have better performance out of it.
Jack
We've implemented 400Mbps shaping with over twenty nested child policies (individual customer shaping and queuing within the 400M) on an NPE-G1 running 12.4(12c). CPU does start to become an issue at that point, and by removing the policy we can reach nearly 600Mbps on the same kit. We run standard ACL, OSPF, EIGRP, VRF Selection, MPLS, MP-BGP, etc. but do not run a full Internet BGP feed on these boxes, so you'll need to subtract that process usage if it applies. I would note that upgrading the box to 12.2(33)SRC caused a 20%+ increase in CPU attributed to the HQF (Hierarchical QOS Framework) process. We decided to stay with the 12.4 train. Cory Ayers CCIE #16874 (R&S), CCIP Director of Network Strategy Education Networks of America