Hello Parthiban,

what really counts is the packet rate not the aggregate rate in Mbps.

There are results in point-to-point GRE+IPSEC solution reference design that would say yes but to be noted they are using many small BW tunnels

http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/P2P_GRE_IPSec/4_p2pGRE_Phase2_external_docbase_0900e4b180a3eff0_4container_external_docbase_0900e4b180ad8740.html

but if I've understood you correctly you have two GRE tunnels per direction one over ISP1 link and one over ISP2 link.

What happens if you use GRE tunnels without IPSec do you still see drops or not?

Data sheet of VAM2+ says:

Data Encryption Standard (DES) standard mode with 56-bit key: Cipher Block Chaining (CBC)
• >>>> 3-Key Triple DES (168-bit) algorithms at speeds up to 292 Mbps
• 128/192/256-bit Advanced Encryption Standard (AES) in hardware
>>>>>• Performance to OC3 full duplex with 300 byte packets
• Up to 5000 tunnels for DES/3DES/AES
• Provides compression with IPSec at no extra overhead (LZS)
• Secure Hash Algorithm (SHA)-1 and Message Digest 5 (MD5) hash algorithms
• Rivest, Shamir, Adelman (RSA) public-key algorithm
• Diffie-Hellman Groups 1, 2 and 5
• Online Insertion and Removal (OIR)

Performance to OC3 full duplex with 300 byte packets this means 149 Mbps of packets of 300 byte

it gives 62,083 pps per direction 124,166 pps aggregate

http://www.cisco.com/en/US/prod/collateral/modules/ps8768/ps7332/data_sheet_c78_48012.html

see troubleshooting tips on configuration guide to check if there are errors in show commands related to VAM2+

http://www.cisco.com/en/US/docs/security/vpn_modules/vam_vsa/vam2plus/installation/guide/vam2p_cf.html#wp68671

Hope to help

Giuseppe