The 2801 is an ISR (Intergrated services router) which depending on your needs could be classed as overkill.
If you do require routing as well as vpn functionality the Pix will do this for you also and wont have a lot of overhead.
A Cisco Pix 501 supports upto 10 concurrent Vpn users
Cleartext throughput: Up to 60 Mbps
Concurrent connections: 7,500
56-bit DES IPsec VPN throughput: Up to 6 Mbps
168-bit 3DES IPsec VPN throughput: Up to 3 Mbps
128-bit AES IPsec VPN throughput: Up to 4.5 Mbps
Simultaneous VPN peers: 10
If you need more bandwidth or if there is a need to expand in the future
The Cisco Pix 506
Cleartext throughput: Up to 100 Mbps
Concurrent connections: 25,000
56-bit DES IPSec VPN throughput: Up to 20 Mbps
168-bit 3DES IPSec VPN throughput: Up to 16 Mbps
128-bit AES IPSec VPN throughput: Up to 30 Mbps
256-bit AES IPSec VPN throughput: Up to 25 Mbps
Simultaneous VPN peers: 25