spec: q66, 260+, 4g ram

SP: works perfectly ok on resolution like 1440x900, 1680x1050, 1920x1200 on high setting
MP: same setting as above works ok BUT as soon as i/people START SHOOTING my frame work gets cut down by half continuously with heavy stuttering
i practically cant engage in any firefight
very very weird issue
welcome any suggestions
thx in advance

you have problems then, its not happening for me.