It's not so simple, your 19" monitor native resolution is needed (if that 1440x900 isnt), new monitor native resolution and fov, maybe i can answer you in 2 weeks :D im arriving.
Your question is reffering to Aspect Ratio, not to Display Size.
Most used variation of Display Resolution for specified Aspect Ratio:
4:3 = 1.3(3):
800 x 600
1024 x 768
1152 x 864
1600 x 1200
5:4 = 1.25:
1280 x 1024
1600 x 1280
16:9 =1.7(7):
40 x 360
720 x 405
864 x 486
960 x 540 qHD
1024 x 576
1280 x 720 HD
1366 x 768 (Very popular; used by 26.33% of steam users)
1600 x 900 HD+
1920 x 1080 Full HD (Most popular; used by 34.54% of steam users; I recommend it for ET)
2048 x 1152
2560 x 1440 QHD
2880 x 1620
3200 x 1800
3840 x 2160 UHDTV
4096 x 2304
5120 x 2880
7680 x 4320 UHDTV
15360 x 8640
16:10 = 1.6:
1280 x 800 WXGA
1440 x 900 WXGA+ (Make me guess your old monitor had 16:10 if You used this resolution)
1680 x 1050 WSXGA+
1920 x 1200 WUXGA
2560 x 1600 WQXGA
I would strongly recommend You to use one of these Display Resolutions for specified Aspect Ratio of Your current monitor.
Your question is reffering to Aspect Ratio, not to Display Size.
Most used variation of Display Resolution for specified Aspect Ratio:
4:3 = 1.3(3):
800 x 600
1024 x 768
1152 x 864
1600 x 1200
5:4 = 1.25:
1280 x 1024
1600 x 1280
16:9 =1.7(7):
40 x 360
720 x 405
864 x 486
960 x 540 qHD
1024 x 576
1280 x 720 HD
1366 x 768 (Very popular; used by 26.33% of steam users)
1600 x 900 HD+
1920 x 1080 Full HD (Most popular; used by 34.54% of steam users; I recommend it for ET)
2048 x 1152
2560 x 1440 QHD
2880 x 1620
3200 x 1800
3840 x 2160 UHDTV
4096 x 2304
5120 x 2880
7680 x 4320 UHDTV
15360 x 8640
16:10 = 1.6:
1280 x 800 WXGA
1440 x 900 WXGA+ (Make me guess your old monitor had 16:10 if You used this resolution)
1680 x 1050 WSXGA+
1920 x 1200 WUXGA
2560 x 1600 WQXGA
I would strongly recommend You to use one of these Display Resolutions for specified Aspect Ratio of Your current monitor.
Cheers.