While Category 5e cables are indeed capable of supporting 1 Gbps speeds, in a high-density environment where alien crosstalk could be a concern, a higher category of cable that offers better shielding and can counteract this type of interference is recommended. Category 6a is specifically designed to reduce alien crosstalk and can support 10 Gbps speeds up to 100 meters, which exceeds the 1 Gbps requirement while also addressing the high-density concern. This makes Category 6a the best choice in this scenario, offering both the necessary speed for 1000BASE-T operations and additional shielding against crosstalk interference. Category 7 and coaxial cables, while also having shielding, are not typically used for 1000BASE-T Ethernet and thus are not the best choice for this particular standard and its connectivity requirements.