Generally, L3 switch has performance, router has features. E.g. 48 port 4948 offers 72 Mpps while the 7200 using NPE-G2 offers 2 Mpps; the 7200 supports NBAR and OER, the 4948 does not, nor does it support direct WAN interfaces (e.g. T1/E1, T3/E3, etc.) or their technologies (HDLC, PPP, frame-relay, ATM, MPLS, etc.).
When working within LANs, the above mentioned 4948 can handle all 48 ports at wire rate, 96 Gbps (duplex), the 7200 can handle up to an OC3, 155 Mbps. Since you often have a large drop in bandwidth from LAN to WAN, the additional features of a WAN router can be of huge benefit.
The larger chassis based solutions, e.g., 6500/7500, offer both LAN performance and WAN support, although even their WAN features aren't quite as rich as the slower routers. They do handle higher speed WAN connections.
Yes you can use a l3 switch for routing , that is what they are for . It depends on your network setup , most l3 switches don't have different interfaces like serial , isdn , atm etc.... If this is all for a local network and you do not need different types of interfaces to tie it all together then you would not need a router . A router is also considerably slower at routing packets than a layer 3 switch in which most packets are switched in hardware at high rates.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...